The specific transport system for lysine is fully inhibited by ammonium in Penicillium chrysogenum: An ammonium-insensitive system allows uptake in carbon-starved cells

The regulation exerted by ammonium and other nitrogen sources on amino acid utilization was studied in swollen spores of Penicillium chrysogenum. Ammonium prevented the L-lysine, L-arginine and L-ornithine utilization by P. chrysogenum swollen spores seeded in complete media, but not in carbon-deficient media. Transport of L-[¹⁴C]lysine into spores incubated in presence of carbon and nitrogen sources was fully inhibited by ammonium ions (35 mM). However, in carbon-derepressed conditions (growth in absence of sugars, with amino acids as the sole carbon source) L-[¹⁴C]lysine transport was only partially inhibited. Competition experiments showed that L-lysine (1 mM) inhibits the utilization of L-arginine, and vice versa, L-arginine inhibits the L-lysine uptake. High concentrations of L-ornithine (100 mM) prevented the L-lysine and L-arginine utilization in P. chrysogenum swollen spores. In summary, ammonium seems to prevent the utilization of basic amino acids in P. chrysogenum spores by inhibiting the transport of these amino acids through their specific transport system(s), but not through the general amino acid transport system that is operative under carbon-derepression conditions.     

Exploring the Relationship between Skeletal Mass and Total Body Mass in Birds

Total body mass (TBM) is known to be related to a number of different osteological features in vertebrates, including limb element measurements and total skeletal mass. The relationship between skeletal mass and TBM in birds has been suggested as a way of estimating the latter in cases where only the skeleton is known (e.g., fossils). This relationship has thus also been applied to other extinct vertebrates, including the non-avian pterosaurs, while other studies have used additional skeletal correlates found in modern birds to estimate TBM. However, most previous studies have used TBM compiled from the literature rather than from direct measurements, producing values from population averages rather than from individuals. Here, we report a new dataset of 487 extant birds encompassing 79 species that have skeletal mass and TBM recorded at the time of collection or preparation. We combine both historical and new data for analyses with phylogenetic control and find a similar and well-correlated relationship between skeletal mass and TBM. Thus, we confirm that TBM and skeletal mass are accurate proxies for estimating one another. We also look at other factors that may have an effect on avian body mass, including sex, ontogenetic stage, and flight mode. While data are well-correlated in all cases, phylogeny is a major control on TBM in birds strongly suggesting that this relationship is not appropriate for estimating the total mass of taxa outside of crown birds, Neornithes (e.g., non-avian dinosaurs, pterosaurs). Data also reveal large variability in both bird skeletal and TBM within single species; caution should thus be applied when using published mass to test direct correlations with skeletal mass and bone lengths.     

Species-specific functioning of the Pseudomonas XcpQ secretin: role for the C-terminal homology domain and lipopolysaccharide

Secretins are oligomeric proteins that mediate the export of macromolecules across the bacterial outer membrane. The members of the secretin superfamily possess a C-terminal homology domain that is important for oligomerization and channel formation, while their N-terminal halves are thought to be involved in system-specific interactions. The XcpQ secretin of Pseudomonas spp. is a component of the type II secretion pathway. XcpQ from Pseudomonas alcaligenes is not able to functionally replace the secretin of the closely related species Pseudomonas aeruginosa. By analysis of chimeric XcpQ proteins, a region important for species-specific functioning was mapped between amino acid residues 344 and 478 in the C-terminal homology domain. Two chromosomal suppressor mutations were obtained that resulted in the proper functioning in P. aeruginosa of P. alcaligenes XcpQ and inactive hybrids. These mutations caused a defect in the synthesis of the lipopolysaccharide (LPS) outer core region. Subsequent analysis of different LPS mutants showed that changes in the outer core and not the loss of O antigen caused the suppressor phenotype. High concentrations of divalent cations in the growth medium also allowed P. alcaligenes XcpQ and inactive hybrids to function properly in P. aeruginosa. Since divalent cations are known to affect the structure of LPS, this observation supports the hypothesis that LPS has a role in the functioning of secretins.     

Preventing metal-mediated oxidative DNA damage with selenium compounds

Copper and iron are two widely studied transition metals associated with hydroxyl radical (˙OH) generation, oxidative damage, and disease development. Because antioxidants ameliorate metal-mediated DNA damage, DNA gel electrophoresis assays were used to quantify the ability of ten selenium-containing compounds to inhibit metal-mediated DNA damage by hydroxyl radical. In the Cu(I)/H(2)O(2) system, selenocystine, selenomethionine, and methyl-selenocysteine inhibit DNA damage with IC(50) values ranging from 3.34 to 25.1 μM. Four selenium compounds also prevent DNA damage from Fe(II) and H(2)O(2). Additional gel electrophoresis experiments indicate that Cu(I) or Fe(II) coordination is responsible for the selenium antioxidant activity. Mass spectrometry studies show that a 1?:?1 stoichiometry is the most common for iron and copper complexes of the tested compounds, even if no antioxidant activity is observed, suggesting that metal coordination is necessary but not sufficient for selenium antioxidant activity. A majority of the selenium compounds are electroactive, regardless of antioxidant activity, and the glutathione peroxidase activities of the selenium compounds show no correlation to DNA damage inhibition. Thus, metal binding is a primary mechanism of selenium antioxidant activity, and both the chemical functionality of the selenium compound and the metal ion generating damaging hydroxyl radical significantly affect selenium antioxidant behavior.     

Biosynthesis and genetic control of isovitexin 2″-O-arabinoside in petals of Silene dioica

In petals of Silene dioica plants, an enzyme has been demonstrated which catalyses the transfer of the arabinose moiety of UDP-arabinose to the hydroxyl group on the 2″-position of the carbon-carbon bound glucose of isovitexin. The presence of this arabinosyltransferase activity is controlled by the dominant allele gl^A. Maximal activity takes place at pH 7.2–7.5; the reaction is stimulated by the divalent metal ions Mg and Mn. For optimal solubilization of the enzyme, Triton X-100 is necessary. Substrate specificity and kinetic behaviour have been investigated.     

Ethanol production from hexoses, pentoses, and dilute-acid hydrolyzate by Mucor indicus

Consumption of hexoses and pentoses and production of ethanol by Mucor indicus were investigated in both synthetic media and dilute-acid hydrolyzates. The fungus was able to grow in a poor medium containing only carbon, nitrogen, phosphate, potassium, and magnesium sources. However, the cultivation took more than a week and the ethanol yield was only 0.2 gg(-1). Enrichment of the medium by addition of trace metals, particularly zinc and yeast extract, improved the growth rate and yield, such that the cultivation was completed in less than 24 h and the ethanol and biomass yields were increased to 0.40 and 0.20 gg(-1), respectively. The fungus was able to assimilate glucose, galactose, mannose, and xylose, and produced ethanol with yields of 0.40, 0.34, 0.39, and 0.18 gg(-1), respectively. However, arabinose was poorly consumed and no formation of ethanol was detected. Glycerol was the major by-product in the cultivation on the hexoses, while formation of glycerol and xylitol were detected in the cultivation of the fungus on xylose. The fungus was able to take up the sugars present in dilute-acid hydrolyzate as well as the inhibitors, acetic acid, furfural, and hydroxymethyl furfural. M. indicus was able to grow under anaerobic conditions when glucose was the sole carbon source, but not on xylose or the hydrolyzate. The yield of ethanol in anaerobic cultivation on glucose was 0.46 g g(-1).